41) This problem asks us the speed measured on Earth of the laser pulse. This problem requires us to know that the speed of light is c ≈ 3 * 10^8 m/s. It is crucial to recognize that this is a trick problem. Many students may think that they need to account for the speed of the spaceship in order to find the perceived speed of the laser. Those students would add the speed of light and the speed of the spaceship.
This is not correct. Many students may think that, by using reference frames, the speed of the laser increases since it is attached to a spaceship traveling at 2 * 10^8 m/s. Due to Einstein's postulates of special relativity, light will always be perceived to travel at about 3 * 10^8 m/s, no matter which reference frame it is measured from. Thus, the light must travel with a velocity c ≈ 3 * 10^8 m/s.
Answer: D
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